Such analytical devices are applied, for example, in process measurements technology or in industrial measurements technology. For example, analytical devices can serve for monitoring and optimizing the cleaning effectiveness of a clarification plant, e.g. by monitoring the activation basin and the clarification plant outlet. Furthermore, analytical devices can be applied for monitoring drinking water or for monitoring the quality of food. Measured variables determined and monitored by analytical devices are, for example, an analyte content of a liquid, e.g. content of ions such as ammonium, phosphate or nitrate, biological or biochemical compounds content, e.g. hormones, or the content of microorganisms. Other measured variables, which are determined by analytical devices in process measurements technology, especially in the area of water monitoring, are e.g. the total carbon content (TOC) or chemical oxygen demand (COD).
Frequently in analytical devices, the sample to be analyzed is mixed with one or more reagents so that a chemical reaction occurs; the chemical reaction is detectable by means of physical methods, for example, through optical measurements. For example, the chemical reaction can affect color of the liquid sample or cause a color change, which is photometrically detectable.
In order to use such an analytical method in industry, it is desirable to provide an analytical device, which automatedly performs the required analytical method and requires as few interventions or maintenance measures by qualified operators as possible. Besides sufficient accuracy of measurement, the most important requirements for such an analytical device are robustness, simple operability and the assuring of sufficient occupational or environmental safety. Since the reagents used for the analysis in part cannot be readily allowed in the water system, their safe disposal likewise plays an essential role.
Semiautomatic and automatic analytical devices are known from the state of the art. These are often relatively complicated in construction and, consequently, susceptible to defects and, as a rule, can be used only by trained operating personnel. Thus, for example, DE 102 22 822 A1 and DE 102 27032 A1 describe online analyzers for analyzing measurement samples. The online analyzers are embodied, in each case, as cabinet devices, in which are arranged a control unit, reagent supply containers, pumps for conveying and dosing a liquid sample and the reagents from the reagent supply containers into a measuring cell as well as a measuring transducer for performing optical measurements on the measured liquid accommodated in the measuring cell and formed, for example, by adding the reagents to the liquid sample. The reagents are conveyed via liquid lines formed by hose connections from the reagent containers and transported into the measuring cell. Correspondingly, used measured liquid is transferred, in turn, to a waste container via a hose connection. If the waste container or one or a number of the reagent supply containers must be replaced, attention must be paid that the hose connections are then reconnected correctly. The hoses and conveyor pumps are susceptible to material fatigue and must likewise be subjected to maintenance or be replaced from time to time.
DE 10 2009 029 305 A1 describes an analytical device for automated determining of a measured variable of a liquid sample, which analytical device includes one or a number of liquid containers for one or a number of liquids, e.g. reagents, a measuring cell for accommodating a measured liquid produced by mixing the liquid sample with one or more reagents and a measuring arrangement for providing one or more measurement signals correlated with the measured variable. Furthermore, the analytical device possesses an electronics unit, which includes a control unit for control of the analytical device and for determining the measured variable based on the measurement signals provided by the measuring arrangement, and has a processing unit controlled by the control unit, which processing unit includes a supply and dosing system for supplying and dosing the liquid sample and liquids from the liquid storer into the measuring cell. The analytical device possesses at least one exchangeable cassette, into which the liquid containers and/or at least parts of the processing unit are integrated.
An advantage of this embodiment is that the liquid containers or wear parts of the processing. unit, such as hoses or wear parts of the supply and dosing system, which must be renewed by operating personnel from time to time, can be arranged in the cassette. For providing new liquids or for replacing the wear parts, a service person must then only replace the “used” cassette having the liquid containers or wear parts to be replaced with a new cassette.
In the examples of embodiments described in DE 10 2009 029 305 A1, the supply and dosing system includes two peristaltic pumps, wherein a first peristaltic pump serves for selectively supplying and dosing a liquid sample from a sample supply, a cleaning liquid from a liquid container or a calibration standard from another liquid container of the analytical device into the measuring cell. A second peristaltic pump serves for supplying and dosing a reagent into the measuring cell. For selecting, in each case, the liquid to be provided through the first peristaltic pump, valves are provided, which, in each case, are correspondingly operated by the electronic control unit of the analytical device. This construction is relatively simple and permits, for example, the integration of wear parts of the peristaltic pumps in an exchangeable cassette. The supplying of a number of liquids by means of one and the same peristaltic pump only allows a limited processing flexibility, however. In general the dosing precision of peristaltic pumps is inferior to those of piston pumps and can significantly change over the period of use of the hose through material aging. The application of a number of individual valves to be operated is, indeed, basically possible without problem, however, a relatively large installation space is required, depending on how the valves are embodied.
An analytical device for the photometric determination of a parameter of a liquid sample subjected to an oxidizing digestion, e.g. the chemical oxygen demand (COD) or the total nitrogen content, is described in document WO 2005/064328 A1. The device includes a number of liquid containers, from which liquids can be fed into a measuring cell by means of a piston pump connected to all liquid containers. A separate valve is associated with each liquid container. The valve can block the liquid path between each liquid container and the piston pump. Thus, for example, only a single valve can be opened, so that only liquid from the associated liquid container is fed into the cylinder of the piston pump. Alternatively, a number of valves can be opened simultaneously, in order to feed a number of liquids simultaneously. In spite of this, the flexibility of the process guidance of the analysis in this arrangement is limited, since it, indeed, basically permits the simultaneous supplying of a number of liquids, however, it is not possible in this arrangement to set individual feed rates for the different liquids or to dose different volumes of the simultaneously supplied liquids into the measuring cell.